Actually not true. You have to pay gains from coin to coin transactions. For example, let's say you buy 1 BTC with $10k. Then you turn the 1 BTC into 10 ETH. Then, later you convert 10 ETH into 1.2 BTC after the conversion rate between the two changes. At that point you have to pay capital gain on the dollar amount of 0.2 BTC, even if you don't convert any BTC back into USD.